OVULE. 



[ 479 ] 



OVULE. 



surface, and project more or less, so as to 

 give it a nodular aspect. They are round 

 closed sacs (fig. 544). Each possesses two 



Fig. 544. 



Graafian vesicle of the pig. , outer, b, inner layer of 

 the fibrous coat ; c, membrana granulosa ; d, liquid con- 

 tained in the vesicle ; e, proligerous disk ; /, ovum with 

 the zona pellucida, yolk and germinal vesicle. 



Magnified 10 diameters. 



coats; the outer is a fibrous and vascular 

 layer, connected with the stroma by some- 

 what lax areolar tissue, and which some 

 physiologists consider as consisting of two 

 layers. It is composed of imperfectly deve- 

 loped nucleated areolar tissue, with nume- 

 rous, somewhat spindle-shaped, formative 

 cells. Lining this is a basement-membrane, 

 which is most distinct in the young vesicles; 

 and within this again is a layer of epithelial 

 cells, constituting the membrana granulosa 

 (fig. 644 c). Next the surface of the ovary, 

 this is thickened and projects inwards, form- 

 ing the proligerous or granular disk, e. Its 

 component cells form several rows; they 

 are roundish -polygonal, about 1-3000" in 

 diameter, with comparatively large nuclei, 

 and frequently contain granules of fat. The 

 ovum is imbedded in this proligerous disk, e. 



The cavity of the Graafian vesicle contains 

 a liquid resembling the serum of the blood ; 

 and in it are found granules, nuclei, and 

 cells, arising from the disintegration of the 

 membrana granulosa. 



When the vesicle bursts or is opened, the 

 ovum escapes surrounded by the cells of the 

 proligerous disk and the adjacent part of 

 the epithelium. 



In those animals in which the amount of 

 stroma present is small in proportion to the 

 size of the vesicles, the ovaries have a race- 

 mose appearance. 



In many of the lower animals, the ovaries 

 are tubular, the ova lying closely packed 

 within them. 



BIBL. Kolliker, Mikr. Anat. ii.; Siebold, 

 Vergleich. Anat. 



OVULE or OVULUM. The name ap- 



plied to the rudiment of the seed of Flower- 

 ing Plants, produced in the ovary or germen 

 during the development of the flower, fer- 

 tilized by the pollen-grains when complete, 

 and afterwards converted into a SEED by the 

 development of the EMBRYO and other 

 secondary structures during the conversion 

 of the ovary into the fruit. For the general 

 conditions of the ovules in ovaries, reference 

 must be made to botanical works. The 

 ovules make their appearance upon the 

 placenta as cellular papillae rising up from 

 its surface, and at first are simple ; this first 

 development, the main feature of the organ, 

 is called the nucleus (figs. 645-547). In 



Fig. 545. 



Fig. 546. 



Fig. 547. 



End 



--P 



Atropous ovules. 



Fig. 545. Young ovule of Chelidonium. n, nucleus ; 

 ch, chalaza. 



Fig. 546. Young ovule of misletoe, consisting of a 

 nucleus only. 



Fig. 547. Young ovule of walnut, consisting of a 

 nucleus, N, with a single coat, S; End, the endo- 

 stome or micropyle. 



Fig. 548. Young ovule of Polygonum. F, funiculus ; 

 P, primine (of Mirbel) ; S, secundine ; Ex, ezostome ; 

 End, endostome. 



Magnified 40 diameters. 



rare cases this remains naked, but in most 

 instances one or two coats are produced, 

 arising as circular folds near the base, and 

 gradually growing up over the nucleus (fig. 

 547), leaving only a small passage at the 

 apex, leading down to the point of the 

 nucleus. When two coats are formed (fig. 

 548), the inner appears first, the outer ori- 

 ginates later and grows up over the inner, 

 and it is generally thicker and more deve- 

 loped. The inner is called the secundine by 

 Mirbel, the outer the primine (figs. 548, 549. 

 552 S, P). The German writers reverse these 

 names, resting on the true order of develop- 



